There was an accident at the G-E LSTG plant in Schenectady long ago; I think it was in the '60s. What failed was an alternator rotor, not a turbine. It failed at 3600 RPM, and pieces of the rotor burst out of the test housing. Three were killed, and (if memory serves) one body was never found.
One man was on top of the housing looking at a meter when it happened.
The alternator rotor is coupled to the main turbine but is not in direct contact with the steam path and therefore the housing is not as resistant. The speed is, of course, the same and therefore a tremendous amount of mechanical energy spinning that. Without more details everything is speculative.